On Sun, 28 Jan 2024 17:42:30 -0800 Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > On Sun, 28 Jan 2024 at 17:00, Linus Torvalds > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > > > mkdir dummy > > cd dummy > > echo "Hello" > hello > > ( sleep 10; cat ) < hello & > > rm hello > > cd .. > > rmdir dummy > > Note that it's worth repeating that simple_recursive_removal() > wouldn't change any of the above. It only unhashes things and makes > them *look* gone, doing things like clearing i_nlink etc. I know, but I already cover the above case. And that case is not what simple_recursive_removal() is covering. I'm worried about what can be opened after a deletion. Not what has already been opened. The simple_recrusive_removal() is the way to clear the dcache on those files and directories that are being removed so that no new references can happen on them. So, I removed the simple_recursive_removal() from the code to see what happened. Interesting, the opposite occurred. # cd /sys/kernel/tracing # echo 'p:sched schedule' > kprobe_events # ls events/kprobes enable filter sched # ls events/kprobes/sched enable filter format hist hist_debug id inject trigger # cat events/kprobes/sched/enable 0 # echo 'p:timer read_current_timer' >> kprobe_events # ls events/kprobes enable filter sched timer Now delete just one kprobe (keeping the kprobes directory around) # echo '-:sched schedule' >> kprobe_events # ls events/kprobes/ enable filter timer Now recreate that kprobe # echo 'p:sched schedule' >> kprobe_events # ls events/kprobes enable filter sched timer # ls events/kprobes/sched/ ls: reading directory 'events/kprobes/sched/': Invalid argument I have no access to the directory that was deleted and recreated. > > But those VFS data structures would still exist, and the files that > had them open would still continue to be open. > > So if you thought that simple_recursive_removal() would make the above > kind of thing not able to happen, and that eventfs wouldn't have to > deal with dentries that point to event_inodes that are dead, you were > always wrong. No but I want to shrink the dentries after the directory is removed. Perhaps something else is the error here. > > simple_recursive_removal() is mostly just lipstick on a pig. It does > cause the cached dentries that have no active use be removed earlier, > so it has that "memory pressure" kind of effect, but it has no real > fundamental semantic effect. I was using it to "flush" the cache on that directory. Nothing more. > > Of course, for a filesystem where the dentry tree *is* the underlying > data (ie the 'tmpfs' kind, but also things like debugfs or ipathfs, > for example), then things are different. Note, tracefs was built on debugfs. Only the "events" directory is "different". The rest of /sys/kernel/tracing behaves exactly like debugfs. > > There the dentries are the primary thing, and not just a cache in > front of the backing store. > > But you didn't want that, and those days are long gone as far as > tracefs is concerned. Well, as long as eventfs is ;-) -- Steve
